DESCRIPTION: (Adapted from Abstract) This is a proposal for a five year renewal of a three year project to examine the extent and mechanisms of exercise limitations after pneumonectomy in dogs. Preliminary data indicate that pneumonectomy is much better tolerated in dogs than in humans and that differences in anatomical distortion of the lung and heart may account for the functional differences between these 2 species. By examining the possible mechanisms whereby the dog can so effectively compensate for the effects of pneumonectomy and the limits of these compensations, further insight may be gained as to how the response might be improved in man. The following specific questions will be addressed in adult foxhounds after extensive lung resections: (1) How does preventing over-expansion affect compensation by the remaining lung? (2) How does a low compliance of the cardiac fossa affect compensation by the heart? (3) How does mediastinal shift affect compensation? and (4) How do morphologic changes correlate with functional compensation? These questions will be addressed in two stages. In stage 1, expansion of the remaining lung and mediastinal shift after right pneumonectomy will be prevented with a silastic balloon, molded to the shape of the right hemithorax and inflated with air or insoluble gas. Volume of air can be adjusted by replacing air in the prosthesis with paraffin or silicone. A control group will undergo right pneumonectomy and balloon implantation without air inflation. In stage 2, limits of compensation will be tested by removing 68 percent of the lungs, either by unbalanced resection (i.e.; right pneumonectomy + left upper lobectomy resulting in mediastinal shift) or by balanced resections leaving equal lung volumes in each hemithorax without mediastinal shift. Comparison of these groups examines the effects of mediastinal shift at a fixed level of expansion in the remaining lung. Compensation will be studied functionally in the awake dog at rest and exercise and morphometrically in the inflation fixed lung after sacrifice.